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Background Knowledge (cont.) ▫HLR: Home Location Register  Users are assigned to specific HLR’s based on their phone number  The central repository of user profile data ▫VLR: Visitor Location Register  Each MSC has a VLR  VLRs save all information of the cellphones in this Location Area

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Introduction Denial of Service attacks on HLR Botnets as small as phones can cause a reduction of throughput of more than 90% Contributions: ▫Attack Characterization and Quantification ▫Reduce Adversary’s Workload ▫Provide Intelligent Control Mechanisms

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Attack Overview (cont.) Different from DoS on the Internet ▫Mobile devices cannot transmit entirely arbitrary requests to HLR ▫Such requests must be made in a manner such that unnecessary traffic or side effects are not generated

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Avoiding Wireless Bottlenecks Max throughput S ▫S is maximized at 37% when G=1 ▫G is the number of transmission attempts per timeslot

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Avoiding Wireless Bottlenecks The offered load, G, also known as ρ, is defined as: ▫λ is the arrival rate in commands per second ▫1/μ is the channel hold time (4.615 ms) ▫ρ = 1/ * 0.37 = 80 transmission per sec

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Avoiding Wireless Bottlenecks The attack would need to be distributed over α base stations: